1. Field of the Invention
The present invention relates generally to an antenna, and more particularly to a multi-band antenna used in a portable electronic device, such as a notebook.
2. Description of the Prior Art
With the development of wireless communication, more and more people hope to own portable electronic devices, such as a notebook, capable of connecting to Internet. The systems of the WLAN (Wireless Local-area Network) and the GPRS (General Packer Radio Service) can make the portable electronic devices, such as a notebook, work in Internet. The GPRS is a wide-area network and the data transfer speed thereof is 30 Kbps˜50 Kbps. The WLAN is a local-area network and the data transfer speed is 11 Mbps. The portable electronic device, such as a notebook can choose different Wireless cards for jointing to Internet.
At present, the WLAN is based on Bluetooth technology standard or IEEE802.11 series technology standard. The frequency band of an antenna is 2.4 GHz and 5 GHz in IEEE802.11 series technology standard, but is 900 Mhz, 1800 MHz and 1900 MHz in GPRS technology standard. So, most antennas used in the notebooks work at the above-mentioned frequency bands in recent years.
PIFA (Planar Inverted-F Antenna) is a kind of minitype antenna usually used in a portable electronic device, such as a notebook. PIFA has compact structure, light weight, perfect impedance match, desired horizontal polarization and vertical polarization, and is easy to achieve multi-bands. So, more and more PIFAs are used in the portable electronic devices.
IEEE802.11 series technology standard comprises IEEE802.11a, IEEE802.11b and other different technology standards. The corresponding frequencies are different because of the different technology standards. So, PIFA usually has two radiating elements for providing two different frequencies.
The two different frequencies of the PIFA basically satisfy the requirements of the frequency band, while the radiating field usually has blind field making the signal not being radiated in some directions because of the characteristics of the two frequencies of the PIFA.
In the prior art, two same PIFAs being mirror image arranged to consist a PIFA system decrease radiating blind field. However, because the two PIFAs are mirror image arranged, a pair of radiating element ends of providing common frequency are mirror image arranged too, the PIFA system cannot distinguish which PIFA being a primary antenna and which being a secondary antenna, thus making the PIFA system occurring self-excitation. The self-excitation influences the natural work of the PIFA system. The radiating fields of the two mirror image arranged radiating elements occur superposition and radiating blind field.
Hence, in this art, a multi-band antenna to overcome the above-mentioned disadvantages of the prior art will be described in detail in the following embodiment.